Targeting Acute Myeloid Leukemia Stem Cells Through Perturbation of Mitochondrial Calcium

Abstract

We previously reported that acute myeloid leukemia stem cells (LSCs) are uniquely reliant on oxidative phosphorylation (OXPHOS) for survival. Moreover, maintenance of OXPHOS is dependent on BCL2, creating a therapeutic opportunity to target LSCs using the BCL2 inhibitor drug venetoclax. While venetoclax-based regimens have indeed shown promising clinical activity, the emergence of drug resistance is prevalent. Thus, in the present study, we investigated how mitochondrial properties may influence mechanisms that dictate venetoclax responsiveness. Our data show that utilization of mitochondrial calcium is fundamentally different between drug responsive and non-responsive LSCs. By comparison, venetoclax-resistant LSCs demonstrate a more active metabolic (i.e., OXPHOS) status with relatively high steady-state levels of calcium. Consequently, we tested genetic and pharmacological approaches to target the mitochondrial calcium uniporter, MCU. We demonstrate that inhibition of calcium uptake sharply reduces OXPHOS and leads to eradication of venetoclax-resistant LSCs. These findings demonstrate a central role for calcium signaling in the biology of LSCs and provide a therapeutic avenue for clinical management of venetoclax resistance.SignificanceWe identify increased utilization of mitochondrial calcium as distinct metabolic requirement of venetoclax-resistant LSCs and demonstrate the potential of targeting mitochondrial calcium uptake as a therapeutic strategy.

STAT3 modulates mitochondrial function and plays a critical role in the survival of leukemic stem cells

“…We additionally demonstrate that STAT3 inhibition is an effective modality to overcome venetoclax resistance, which aligns with prior work that has demonstrated the importance of mitochondrial calcium in LSCs. 19 In conclusion, we show STAT3 is highly expressed in AML cells, and inhibition of STAT3 results in decreased OXPHOS, decreased mitochondrial calcium, decreased cell viability, and impaired engraftment potential. We additionally describe a novel role of STAT3 which interacts with VDAC1 in the mitochondria.…”

“…34,35,44,45 Additionally, mitochondrial calcium homeostasis has been shown to be important for LSCs in AML. 19 To determine the potential effects of STAT3 inhibition on mitochondrial calcium flux in AML, we performed calcium assays with Rhod-2 AM staining. We found that pharmacologic (Stattic) inhibition of Molm-13 cells significantly decreased levels of mitochondrial calcium (Figure 4D and Figure 4E).…”

“…[12][13][14] While Bcl-2 inhibition with venetoclax (Ven) in combination with the hypomethylating agent (HMA) azacitidine has demonstrated selectivity for LSCs via inhibition of OXPHOS, 13 resistance frequently develops via alterations in mitochondrial metabolism or activation of alternative antiapoptotic pathways. [15][16][17][18][19] Further, prior studies of patients who progress after frontline HMA/Ven have shown very poor outcomes, with a median survival following failure of HMA/Ven of 3 months or less. 20,21 New strategies targeting LSCs via their reliance on OXPHOS are of significant interest and have been described in several reports, 7,13,22 however further research is needed to elucidate the mechanisms underlying these observations.…”

Nutrient-sensitizing drug repurposing screen identifies lomerizine as a mitochondrial metabolism inhibitor of chronic myeloid leukemia

“…One limitation in our study is that the concentration we used in our in vivo study (1 to 2 μM) is higher than what has been administered to humans at a dose of 40 mg by oral administration. In addition, it would be of interest how lomerizine treatment compares with pharmacological inhibition of the mitochondrial calcium uniporter, which may provide an alternative option for inhibiting mitochondria Ca 2+ influx and OXPHOS in leukemic cells (89). Another limitation is that we did not confirm that lomerizine treatment inhibited OXPHOS in bone marrow-located leukemic cells, which may have reduced mitochondrial metabolic activity because of reduced oxygen concentrations compared with classical tissue culture conditions.…”

Targeting Metabolic Dependencies in Acute Myeloid Leukemia: A Dual Strategy using Arsenic Trioxide and Artesunate

“…We also evaluated the effect of ART in combination with venetoclax (VEN, BCL-2 inhibitor) because recent studies have established that inhibition of SERCA3 overcomes VEN resistance by interfering with Ca 2+ signaling pathways 29 . Additionally, a specific inhibitory effect of ART on SERCA3 activity has been shown in different cellular models, consistent with its original proposed antimalarial mechanism of action as a SERCA(PfATP6) inhibitor.…”